Light-sensitive device



June 19, 1934. s. RUBEN LIGHT SENSITIVE DEVICE Original Filed June 50, 1930 3 Sheets-Sheet. l

ATTORNEY June 19, 1934. s RUBEN Re. 19,218

LIGHT SENSITIVE DEVICE Original Filed June 50, 1930 3 Sheets-Sheet 2 F f APAC/74mm* clica/f FREQUENCY /N CVCLS INVENTOR SAMUEL Z/EE/V ATTORNEY June 19, 1934. I .s. RUBEN LIGHT SENSITIVE DEVICE original Filed June so, 19:50 s sheets-sheet` s w m N l z m m ma e Eur/ML v ALKAL//v/TV R POW, v /vc ws/w;

INVENTOR SAMUEL Reissued June 19, `1934 UNrrEb STATES LIGHT-SENSITIVE DEVICE Samuel Ruben, New Rochelle, N. Y., assigner to Ruben Tube Company, New Rochelle, N. Y., a corporation oi.' Delaware Original No. 1,941,494, dated January 2, 1934, Serial No. 464,838, June 3Q, 1930. Application for reissue March 31, 1934, Serial No. 718,472

zz claims.

1928; S. N. 331,943 led 11 January 1929; S. N'.v

347,726 filed 16 March 1929; S. N. 412,077 led 6 December 1929 (now `IPatent No. 1,941,493,

dated January 2, 1934) and S. N. 424.509 filed 30 January 1930.

One of the objects of ...the invention is to provide a light-sensitive device which will respond uniformly to light variations throughout the visible range and at audio frequencies. f

Another object of the invention is to provide a light-sensitive device which will operate without material electrolytic action.

'Another object of the invention is to provide a light-sensitive device which will operate 4with- 20 out material local chemical effects.

Still another object of the invention is to provide a light-sensitive cell which is adaptable to quantity production with uniform electrical characteristics.

a light-sensitive cell which has substantially no local chemical or electrolytic effects during nonuse thereof.

A further object of the invention is to provide a. light-sensitive device which has a minimum Still another object of the invention is to provide a light-sensitive device having a low impedance.

A still further object of the invention is to provide an inexpensive light-sensitive cell which is very simple, has few parts, and is capable of withstanding extremely hard usage with substantially no effect upon the operation thereof. Other objects ofthe invention andobjects relating particularly toN the methods of constructing the various parts fand to the circuit for using the device will be apparent as the description of the invention proceeds.

60 As disclosed in my United States Letters Patents 1,694,189 and 1,694,190, cuprous oxide, un der certain conditions, is light sensitive. I have now found that if properly prepared and used in cooperation with other suitable materials, that it is not only light sensitive in the ordinary sense,

Another object of the invention is to provide,

(Cl. 13G- 89) but it may be made to respond to high frequency light variations, such as in the order of 6000 cycles. In this invention, the light-sensitive electrode itself comprises a copper base having a thermally-integrally-formed cuprous oxide surface. This electrode is positioned in a container filled with a conductive medium in such a manner as to receive light thrown upon the cuprous oxide surface. A cooperating electrode formed 'of a suitable metal is positioned in proximity to 65 the light sensitive electrode.

I have found by careful experimentation that some of the factors which may aid in attaining the objects stated above may be outlined as follows:

1. The copper-cuprous oxide electrode should be etched.

2. The conducting medium or electrolyte is preferably one having an acidic reaction or a tendency to form an acidic solution of 'a salt. 75

3. The conducting medium may be such that it will not chemically dissolve the light-sensitive material to form a surface product which might prevent light from reaching the light-sensitive material due to the lm formed upon it or due 50 to the light absorption of the conducting medium.

4. The metal serving as the cooperating electrode for the light-sensitive material maybe chosen Aso that there is a minimum difference o1' potential between it and the light-sensitive elec- 8 trode when mounted in the device. Thus chemical eifects or electrolytic effects either in the dark, or when not used, or where a conductive circuit is employed may be maintained at a minimum 5. The conducting medium may be such as not to appreciably dissolve or otherwise chemically react with the cooperating electrode thus avoiding the'formation of a surface product or a polarization potential. e

6. The conducting medium may also preferably be capable of maintaining the sensitive condition of the light-sensitive surface.

7. The conducting medium may also be chemically stable at all times whether in use or not in use and itmay preferably have a high decomposition potential.

8. Where a liquid ,conducting medium is used the concentration thereof may preferably be 105 within certain definite limits because if too weak it may oii'er too high an impedance in the circuit and Vi!! too strong itl might attack the lightsensitive surface and form a surface product thereon thereby destroying the lightsensitive 1m quality thereof or it may produce -a light absorbing compound in the conductingv medium.

9. Where the conducting medium has the quality of absorbing light a minimum of light may be absorbed by placing the light-sensitive electrode as near as possible to .the window or light admitting opening.

The invention has been illustrated in the acy companying drawings in which: i

Fig. 1 is a sectional side elevation of a lightsensitive cell embodying the invention and showing the'circuit connections therefor;

Fig. 2 is a sectional elevation through the light-sensitive element shown in Fig. 1:

Fig. 3 is a perspective view of the light-sensitive element shown in Fig. 1; v

Y Fig. 4 isa diagrammatic representation of a conductive circuit for the lightsensitive cell;

Fig. 5 is a pair of graphs illustrating the difference in lifeof the'light-sensitive cell when connected intwo different kinds of circuits;

Fig. 6 is a graph showing the output difference between two cuprous oxide electrodes, one etched and the other unetched; l

Hg. 'i is a graph showing the diiferentleflects of conducting mediums for the cellhaving acidic and basic reactions;

Fig. 8 is a series of graphs illustrating the effect on the life of the cell of a number of dierent acids used for theconductive medium;

Fig. 9 is a graph showing the eil'ect of a cobalt chloride solution as the conducting medium for use inthe cells: and

Fig. 10 is a series of graphs illustrating the effects with the cell in a conductive circuit of a plurality of different metals for-'the cooperating In Fig. 1 I- have shown a convenient type of light-sensitive cell in which a casing 10 of suitable dielectric material such as bakelite may be -provided with an opening 11 which is threaded -on the inner side thereof to receive the threaded inwardly extending portion 12 of a rim 13. A

` it. The cooperating electrode 20 may comprise a pin having a threaded portion 2l which may The light-sensitive be threaded into a hole provided for that pur"- pose-in the casing wall at the basethereofas indicated. l I

surface is preferably formed 'fromacopperbasa'suchasisdisclosedinmy co-pending application B. N. 301,684 filed 23 August 1928 in which -is shown a light-sensitive electrode composed of copper having a thermally integrally-formed cuprous oxide layer, a co-operating electrode suchaszincormagnesiumand an electrolyte containing cobalt chloride. Thus the copperdisc25 (FIgJlwhichforms th electrode 18ispreferablyelectrolyticcopperandmaybe formed with the' foot `lli provided wltha hole 21 to secure the electrode in position.` The disc maybelheatedinafurnaceinairtoapproximately 1000 C. andfor a period of time sufficient to form a coating 28 of cuprous oxide of desired thickness on one side thereof. The furnace may then be turned ci! and the electrode may be allowed to cool down with the furnace till it reaches room temperature. The extreme outer surface of the oxide may take on an extra atom of omen to the molecule so that it be. comes cupric oxide instead of cuprous oxide and as cupric oxide does not appear to be as sensitive to light and is opaque I prefer to remove all traces of the cupric oxide by immersing the electrode in a bath of hydrochloric acid. After this treatment the electrode is preferably treated to remove the product of the hydrochloric acid reaction as for example by immersing it in concentrated nitric acid. The nitric acid may then `be removed by 'washing the electrode with distilled water.

I have found that by etching the surface of the light-sensitive material to expose its crystalline structure it will respond to very much higher frequencies than when the surface is not etched and the difference between an etched and an una 10% solution of sulphuric acid, appears to not 110 vonly increase the absorption surface or actual working area of the electrode but it seems to help prevent localized voltaic and photo-chemical effects. The etching preferably should be as uniform as possible in order to prevent inactive areas which reduce the sensitivity of the cell and perhaps cause local circuits which shorten the life thereof. When the etching has been completed a'dense homogeneous layer of crystalline cuprous oxide is left on the surface of the copper disc and after the surface has been cleansed with distilled water and when all other portions 'of the disc have been covered by an insulating paint 29 such as'asphaltum paint the electrode is ready to mount in the'light-ensitive cell.

A photo-sensitive electrode comprising a copper base having a thermally-integrally-formedcuprous oxide layer. chemically etched to expose the crystalline structure so as to give an emcient response to light modulations of highispeed, is disclod in- 'my copending application S. N. 331,943'i1led 11 January 1929. A similar etching is also shown in my co-pending application S. N. 412,07Inled 8 December 1929.

'Ihecooperating electrode20maybe ofany desiredmetal orcompoundas willbehereinafter described depending on Athe type of light-sensitive materialused and the conductingmedium.

In Fig. 1 the light-sensitive cell isshown connected in series with a condenser 30 and primary s1 ora transformer sztneseeondsryss or'wmeu maybeconnectedtothe inputofanampliiler nect current flow through the light-sensitive cell f the electrodes 16 and 2 0 and therefore any electroLvtic or electro-chemical ac *tions between the electrodes.

Figureshows outputc1n'vesinwhich,in150 one instance, the cell is directly or conductively' coupled to the output transformer as shown in Fig. 4, as compared, in the other instance, to a cell which is coupled to the output transformer through a capacitance as shown in Fig. 1.

The potential difference of the cell is measured on the ordinate and the time in hours is measured on the abscissa. It will be noted that in a conductive circuit the potential difference falls down practically to zero at the end of 100 hours while ina capacitance circuit the maximum potental diierence' is maintained even beyond 1,000 hours. These figures are based on a light-sensitive electrode having an area of about 3A of a square inch and would be diierent with electrodes of different areas or where different load resistances were used.

In Fig. 4 the primary winding 34 of a transformer 35 is shown connected directly across the terminals of the light-sensitive cell so that any potential difference generated between the elements oi' the cell will cause current to flow in the circuit through the winding 34 and therefore through the conducting medium between the light-sensitive "elements and the cooperating element. With this circuit there will be' a tendency for velectrolytic action between the electrodes but suitable choice of a cooperating electrode as well as the conducting medium will keep such action to a minimum.

By experiment I have found that a conducting medium with a slightly acidic action is preferred for response to audio frequencies and for giving a long life to the cell. If an organic acid solution of about one-half percent concentration is used rfor the conductive medium a cell with a cuprous oxide light-sensitive elec trode suchasshown in Fig. 1 will give excellent dynamic response. tions S. N. 412,077, filed 6 December 1929 and S. N. 424,509 illed 30 January 1930, an electrolyte containing .a weak solution of an organic acid such as citric, butyric or oxalic acid, is

' dynamic res described. This response is indicated in Fig. 10

where a graph showing the percentage of con-k centration of the acid solution is measured along the abscissa and the diierential potential response is measured on the ordinate. As the 'acid is increased up to one-half of one percent the potential of the cell increases to a maximum point giving good results and then if potassium hydrate is added slowly to neutralize the acid the potential difference falls off as indicated in the curve until when the solution is substantially neutral it has reached a point so as to be barely perceptible. g

This diil'erential potential represents the pnse of the cell under lniluence of modulated light at audio frequencies. When more potassium hydrate is added so as `to give the solution a basic reaction there appears to be substantially no diierential potential at all. In

the case of the cuprous oxide light-sensitive materiall this would appear to indicate that the 'contact potential diierence of the oxide is opposite in an alkaline solution to that when it is in an acid solution probably due to the hydrogen ion content of the electrolyte, or due perhaps to the asymmetrical Acharacteristic of the cuprous oxide layer on the copper electrode, for instance the uni-lateral conductivity thereof, and the current` flow or response to light is blocked. If an external source of potential is applied with its cathode connected to the cuprous oxide in a weak alkaline solution a response can be ob- In my copending applica-k tained but with a short life due to electrolytic eiiects..

If after the output has fallen to zero more acid is added it maybe caused to rise to the normal value again. I have checked this result by starting with a basic solution as indicated by the graph of Fig. 7 and adding lactic acid `until the basic solution was neutralized. At this point the output potential of the cell begins to rise and as the acid content is increased the output rises until it reaches its high point similar to that already described in connection with Fig. 10. However as rthe acid is increased in the solution a point is reached when it begins to attack the light-sensitive electrode. This causes vthe voltage output to decrease rather rapidly due of the cell and the horizontal concentration ofv the acid. As has been stated before when the acid becomes too strong it attacks the'lightsensitive surface causing a diminution of theresponse thereof. From an inspection of the graphs it will be seenv that an inorganic acid such as hydrochloric; nitric, sulphuric, hydroiiuoric, hydrobromic, hydroiodic, and phosphoric acid causes the life of the Icell to fall oi by attacking the light-sensitive electrode at relatively low concentration of the acid. The organic acids perinit a longer life with greater concentration and the following are indicated by the graphs in the order of their efl'ect upon the life of the cell: oxalic acid, formic acid, acetic acid, butyric acid, citric acid, and lactic acid, the latter apnearing to permit the greatest concentration without attacking the light-sensitive material.

Other conductive solutions may be used ii desired such .as chlorides, iodides, fluorides, and bromides, of sodium, potassium, magnesium, beryllium, aluminum, strontium, rubidium, csium, lithium, and others including the chlorides of iron, nickel, and cobalt. All of these salt solutions appear to be operable in a conducting circuit such as is shown in Fig. 4 but cobalt chloride is preferably the one operable in a capacitance circuit.

Fig. 9 shows a graph similar to those of Figs. 10 and 7 but illustrating the operation of a cell with cobalt chloride. As the -concentration of cobalt chloride increases a point is reached where the pink color of the cobalt chloride begins to absorb the light and thereby cut down the potential difference in the cell. If the cobalt chloride is made basic' by the addition of potassium hydrate the output potential drops down to zero as in the case illustrated in Figs. 10 and 7.

Where a capacitance circuit is used there ap' pears to be very little difference in the outputtof the cell when different metals are used for the cooperating electrode but`when the cell is used in a conductive circuit the metal outjof which the cooperating electrode is made appears to have faces used in a conductive circuit with different metals for the cooperating electrodes. In this figure it will be noted that the metals are indicated'in the order of their potentials as follows: zinc, iron, lead, nickel and copper. From actual experiment the voltage output for these different metals was as follows: 1. v

Volts Zinc 0.98 Iron 0.59 Lead 0.50 Nickel 0.13 Copper 0.10

When the cell is operating in a conductive cir- I, cuit and with an electro-positive electrode, such' as zinc, the operation of the cell is somewhatV different than'a capacitance circuit. In such an arrangement the cell acts more like a valve,

for the zinc generates a large potential with rer.

. and' with hydroiiuoric acid/1.08 volts was gen- The me or a. ceu or this type appears to dependon the area of the photo-sensitive electrode and upon the potential difference between that elec' trede and the cooperating electrode. Thus with a cell having a zinc cooperating electrode the life Y is shorter than one having a nicki electrode.

Operation in a capacitance circuit is highly desirable 'because for eillcient operation ina conductive circuit with the external resistance equal to the cell resistance due to electrolytic effects with both dark and light current a cell with an area of one square inch of exposedsurface may have a life of about continumis hours. Where the cell so connected is allowed tostand without la load for periods of time the'layer Vof cuprous oxide and copper that is formed may slowly dissolve into the electrolyte so that the cell is recuperated. The life of the cell will then depend on the number of recuperation periods and the lengths of these periods as compared with the lengthsoftheoperatingperiodsandboth of the electrodes are slowly dissolved into the electrolyte. Another -undesirable feature of depending X upon the chemical restoration of the photo-sensiraars of eens havihsuprous onde iight-sensitive sur.

of electrolytic effects, reduction of sensitivity, or change in initial characteristics. y

The use of capacitance coupling also prevents current iiow and allows the cell to remain in the amplifier. circuit without having to be electrically disconnected when not in use which is apparently necessary with the photo-voltaic cell or a cuprous oxide contact potential cell in a conducting circuit.

I have indicated above that acids may be Aused inthe'cell andalsothatcertainsalts maybe -used to advantage and I have discovered that in`mf some instances a high output could be obtained without increasing the chemical attack on the cuprous oxide surface, where it is used, if instead of using solely an acid a combination of the acid and a salt of theacid, especially a copper salt, is used, for example a solution of lactic acid and cuprous lactate, or acetic acid and cuprous acetate, or-citric acid and copper citrate, but in all these combinations I prefer to keep the salt content of the solution to a relatively low value as it tends to increase the absorption of light.l The proper concentrations of acids, however, gives as good if not better results and eliminates light absorptionto a large extent. The weak organic acidssuch as lactic, acetic, or citric acid, .in the order named, give the longest life and the ,inorganic acids unless diluted to percentages much less than one-half of one percent chemically aiect the life of the cell. In general the life is dependent upon the rate of attack of the acid on the light-sensitive material. This also applies to organic acids for if they are too concentrated (more than two percent) they may chemically cutting down the life of the ,there is described a cell utilizing the thermallyformed copper-cuprous oxide light-sensitive'electrode in combination Vwithan electrode which is such salts is shown in the accohmpanying table: 13b

'Ihavefoundthatoneofthereasonswhy ,the

=output of a cell drops over a period of time: as

has already been pointed out above'. is the chemical attack of the electrolyte on the light-sensitive'surface especiallyif a strong acid isused whichl producesa small amount of cuprous salt y 'such as cuprous acetate having a blue coloring and therefore increasing the absorption of light.

lltisforthisreasonthatIpreferawklactic acid electrolyte because it reacts to a minimum amount with the cuprous oxide electrode and the cooperating electrode. This action may be further minimized by using ethyleneglycol of glycerine for the acid diluting material instead oi' water. This will materially reduce the chemical effect and consequent cause of light absorption. 'Ihis is also one of the reasons why I prefer to keep the light-sensitive surface as close as possible to the glass window as stated above. In my co-pending application S. N. 306,607 led 17 September 1928, there is described a cell utilizing a thermally formed light sensitive coppercuprous oxide electrode immersed in an electrolyte containing glycerine. In my co-pending application S. N. 412,077 filed 6 December 1929, is disclosed an electrolyte containing glycerine or ethyl glycol.

Certain metallic salts when dissociated may form acidic salts, as cobalt chloride which can dissociate into hydrochloric acid.

A cell constructed in accordance with the principles as above described has a relatively low im- .pedance which may be in the neighborhood of 1500 ohms.

lMany modifications of the invention may be resorted to' without departing from the spirit thereof and I do not therefore desire to limit the invention except as such limitations occur in the appended claims.l

What I claim is:

1. A photo-voltaic cell havinga container, a photo-sensitive electrode comprisingl a copper base having a thermally-integrally-formed, etched, crystalline cuprous oxide surface, a cooperating electrode and an electrolyte in contact` with both electrodes.

2. A photo-voltaic cell as described in claim 1 in which the cooperating electrode is composed oi' copper.

3. A photo-voltaic cell as described in claim 1 in which the cooperating electrode is composed oi' zinc. v

4. A photo-voltaic cell as described in claim 1 in which the cooperating electrode is composed of a material electronegative with respect to said cuprous oxide.

5. A photo-voltaic cell having a container, a photo-sensitive electrode comprising a copper base having a thermally-integrally-formed, etched, crystalline cuprous oxide surface, a cooperating electrode and an electrolyte containing an acid.

6. A photo-voltaie cell as described in claim 5 in which the electrolyte contains lactic acid.

7. A photo-voltaic cell having a container, a photo-sensitivey electrode comprising a copper base having a thermally-integrally-i'ormed, etched, crystalline cuprous oxide surface, a cooperating electrode and an electrolyte containing a haloid solution in contact with both electrodes.

8. A photo-voltaic cell as described in claim 7 in which the cooperating electrode is composed of copper.

9. A photo-voltaic cell having. a container, a photosensitive electrode comprising a copper base having a thermally-integrally-formed, crystalline cuprous oxide surface, a cooperating electrode and an electrolyte containing cobalt chloride in contact Awith both electrodes.

10. A photo-voltaic cell having a container, a photo-sensitive electrode comprising a copper base having a thermally integrally formed, crystalline cuprous oxide surface, a cooperating electrode and an electrolyte in contact with both electrodes.

11. A photo-voltaic cell as described in claim 10 in which the electrolyte has an acidic reaction.

12. A photo-voltaic cell as described in claim l0 in which the electrolyte has a tendency to form an acidic solution of a salt.

13. A photo-voltaic cell as described in claim 10 in which the electrolyte is composed of one of the compounds ethylene glycol and glycerine, containing a conductive medium.

14. A photo-voltaic cell as described in claim 10 in which the electrolyte is composed of one of the compounds ethylene glycol and glycerine, and a weak acid.

15. A photo-voltaic cell as described in claim 10 in which the electrolyte is composed of one of the compounds ethylene glycol and glycerine, and an organic acid.

16. A photo-voltaic cell as described in claim 10 in which the electrolyte is composed of one oi'- the compounds ethylene glycol and glycerine, and an inorganic acid.

17. A photo-voltaic cell as described in claim 10 in which the electrolyte is composed of one of the compounds ethylene glycol and glycerine and an organic acid of a concentration less than 2%.

18. A photo-voltaic cell as described in claim 10 in which the electrolyte is composed of one of the compounds ethylene glycol and glycerine and an inorganic acid ofv a concentration less than 1/ 19. A photo-voltaic cell as described in claim 10 in which the cooperating electrode is Icomposed of a material electropositive with respect to said cuprous oxide.

20. A photo-voltaic cell as described in claim 10 in' which the cooperating electrode is composed oi?v zinc.

21. A photo-voltaic cell as described in claim 10 in which the cooperating electrode is composed of iron.

22. A photo-electric cell having a copper anode with a thermally-integrally-formed layer of cuprous oxide and a cooperating cathode electropositive with respect to the anode, immersed in an electrolyte composed of cobalt chloride.

SAMUEL RUBEN. 

